Cellulosic paperboard must reconcile several conflicting properties to be useful for the manufacture of plates, cups, bowls, canisters, French fry sleeves, hamburger clam shells, rectangular take-out containers, and related articles of manufacture. The paperboard has to have good thermal resistance, improved formability, and, to be economical, reduced board weight, or, for premium applications, increased container rigidity. The fiber weight (hereinafter xe2x80x9cwxe2x80x9d) of the paperboard should be at least about forty pounds for each three thousand square foot ream. Fiber weight is the weight of fiber in pounds for each three thousand square foot ream. The fiber weight is measured at standard TAPPI conditions which provide that the measurements take place at a fifty percent relative humidity at seventy degrees Fahrenheit. In general, the fiber weight of a 3000 square foot ream is equal to the basis weight of such a ream minus the weight of any coating and/or size press. The fiber mat density of the paperboard of this invention is in the range of about 3 to 9 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch. The preferred fiber mat density is in the range of about 4.5 to 8.3 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch. To achieve the superior properties of our novel cellulosic paperboard, it has been discovered that the board at a fiber mat density of 3, 4.5, 6.5, 7, 8.3, and 9 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, should have a GM Taber stiffness of at least 0.00716 w2.63 grams-centimeters/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, and a GM tensile stiffness of at least about 1890+24.2 w pounds per inch. The preferred GM Taber stiffness value for paperboards having the fiber mat density given above is 0.00501 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, and the GM tensile stiffness is 1323+24.2 w pounds per inch. The high GM Taber stiffness values listed are desired to facilitate the bending of the paperboard into the aforementioned articles of manufacture and to provide these articles with greater rigidity. Likewise the high GM Taber and GM tensile stiffness prevents the plates, cups, and other articles of manufacture from collapsing when used by the consumer. The articles of manufacture can suitably be prepared from either one-ply or multi-ply paperboard as disclosed herein. The present invention provides one-ply and multi-ply paperboard comprising (a) predominantly cellulosic fibers, (b) bulk and porosity enhancing additive interspersed with the cellulosic fibers in a controlled distribution throughout the thickness of the paperboard, and (c) size press applied binder coating optionally including a pigment adjacent both surfaces of the paperboard and penetrating into the board to a controlled extent. The amount of size press applied is at least one pound for each three thousand square foot ream of paperboard having a fiber mat density of about 3 to below 9 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch. For boards having a fiber mat density of 9 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch or a greater density, the amount of size press applied should be at least six pounds for each three thousand square foot ream. The overall fiber weight of the paperboard is at least 40 lbs. per 3000 square foot ream, suitably 60 to 320 lbs. per 3000 square foot ream, preferably 70 to 240 lbs. per 3000 square foot ream, most preferably 80 to 220 lbs. per 3000 square foot ream, and the distribution of the bulk and porosity enhancing additive is controlled so that at least twenty percent of the additive is distributed in the central layer and not more than 75 percent of the additive is distributed on the periphery of the paperboard with no periphery having more than twice the percent of the additive distributed in the central layer of the paperboard. The penetration of the size press applied binder and optionally pigment coating into board is controlled to produce a cellulosic fiber board web having at a fiber mat density of 3, 4.5, 6.5, 7, 8.3, and 9 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, a GM Taber stiffness respectively of at least 0.00716 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, and GM tensile stiffness of about 1890+24.2 w pounds per inch. The preferred GM Taber stiffness for the paperboard of this invention having a fiber mat density of 3, 4.5, 6.5, 7, 8.3, and 9 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch is 0.00501 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, and the preferred GM tensile stiffness is 1323+24.2 w pounds per inch. The GM tensile and GM Taber values for the web and one-ply board are the same. For multi-ply board the overall paperboard GM Taber stiffness and GM tensile stiffness are the same as for a one-ply paperboard. The aforementioned combination of GM Taber stiffness and GM tensile stiffness provides a paperboard which can readily be converted to useful high quality cups, plates, compartmented plates, bowls, canisters, French fry sleeves, hamburger clam shells, rectangular take-out containers, food buckets, and other consumer products and useful articles of manufacture including cartons and folding paper boxes. This paperboard is also particularly suitable for the manufacture of heat insulating paperboard containers having on their wall surfaces a foamed layer of a thermoplastic film such as a polyethylene.
This invention relates to an improved paperboard, to improved shaped paperboard products, and to methods of making such paperboard and shaped paperboard products including heat insulating paperboard containers such as cups having as their wall surface a foamed layer of a thermoplastic film. More particularly, this invention is directed to an improved bulk-enhanced paperboard, to methods of making such an improved paperboard, and to shaped paperboard products made from such improved paperboard.
Prior art has not been able to produce a paperboard having the GM Taber stiffness and GM tensile of the board of this invention. Prior art bulk-enhanced paper products, such as those disclosed in U.S. Pat. Nos. 3,941,634 and 3,293,114, resulting from the addition of expandable microspheres and other bulk enhancing additives and methods for making such paper suffer from a number of drawbacks. For example, one persistent problem in such papers is poor retention of the expandable microspheres or other bulk enhancing additives on the embryonic paper web made in the course of manufacturing the paperboard. This poor retention results in relatively low bulk enhancement of the resulting paperboard per unit weight of bulk enhancing additive added, making the enhancement process unnecessarily costly. A further problem resulting from the poor retention of microspheres and other bulk enhancers experienced in prior art bulk enhancement methods is fouling of the papermaking apparatus with unretained microspheres and other bulk enhancing additives.
A related problem associated with the addition of microspheres and other bulk enhancing additives in the papermaking process is their uneven distribution within the resulting paperboard. Paperboards prepared using prior art enhancement techniques have exhibited a decided asymmetry, with microspheres and other bulk enhancing additives migrating to one of the outer surfaces of the paper web and causing undesired roughness in the surface of the finished paper and hence interference with the smooth and efficient operation of the papermaking apparatus.
The void volume provided by the microspheres reduces the rate of thermal transfer within the paper, which is desirable in many applications. However, the asymmetric distribution of microspheres experienced in the prior art produces uneven thermal insulating characteristics.
In addition, prior art has not created a satisfactory bulk-enhanced paperboard. Prior art products tend to have low thermal insulative properties. The excessive concentration of microspheres at the paper surface creates dusting, which interferes with the operation of printing presses in which the paperboard is used. The printability of the paperboard itself, that is, the satisfactory retention of printed matter on the paperboard, is also adversely affected by such dusting.
Prior art attempts at addressing the above and other drawbacks and disadvantages of paper containing microspheres and other bulk enhancing additives have been unsatisfactory and have had their own drawbacks and disadvantages. For example, in U.S. Pat. No. 3,941,634 Nisser attempts to address the inadequate retention and non-uniform distribution of microspheres by sandwiching the microspheres between two paper webs formed on two wire screens. The introduction of the second paper web adds complexity and expense to the papermaking process. Furthermore, the Nisser process generally does not optimize thermal insulation characteristics because it does not produce a sufficiently even distribution of microspheres within the resulting paper. The same problems are encountered in U.S. Pat. No. 3,293,114 and make the use of current bulk-enhanced papers in thermal insulation applications problematic.
Another attempted solution to the above and other drawbacks and disadvantages of paper containing microspheres has been to employ a surface sizing formulation to xe2x80x9cburyxe2x80x9d the microspheres which would otherwise be found on the outer surface of the resulting paper. See for example, Development of a Unique Lightweight Paper, by George Treier, TAPPI Vol. 55, No. 5, May 1972. This approach, again, has failed to achieve the desired distribution and retention of microspheres, as well as other desirable paper characteristics. In addition to the expensive film forming materials described in the George Treier article, the Treier process increases the complexity and cost of manufacturing paperboard.
The process of making cups, plates, bowls, canisters, French fry sleeves, hamburger clam shells, rectangular take-out containers, food buckets, and other shaped paper articles by deforming bulk-enhanced paperboard to create the desired shapes also suffers from various drawbacks and disadvantages. Such paperboard is generally rendered substantially less deformable after being bulk-enhanced by the additions of microspheres. This reduced deformability interferes particularly with top curl forming in rolled brim containers made from bulk-enhanced paperboard. It also interferes with the drawing of cups, plates, bowls, canisters, French fry sleeves, hamburger clam shells, rectangular take-out containers, and food buckets, the reduced deformability in forming dies, and all other applications requiring deformation of bulk-enhanced paper generally and bulk-enhanced paperboard in particular.
Accordingly, there is a need for an improved, bulk-enhanced paperboard which retains a higher percentage of added bulk enhancers in the center layer of the board than has heretofore been achieved. There is a need for a cellulosic paperboard which at a fiber mat density of 3, 4.5, 6.5, 7, 8.3, and 9 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, has a GM Taber stiffness of at least about 0.00716 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, and a GM tensile of 1890+24.2 w pounds per inch. The preferred GM Taber stiffness for the paperboard of this invention having a fiber mat density of 3, 4.5, 6.5, 7, 8.3, and 9 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch is 0.00501 w2.63 grams-centimeter/fiber mat density1 63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, and the preferred GM tensile stiffness is 1323+24.2 w pounds per inch. At a fiber mat density of 3, 4.5, 6.5, 7, and 8.3 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, GM Taber stiffness is 0.00120 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00062 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00034 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00030 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, and 0.00023 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch; the GM Taber stiffness is 1890+24.2 w pounds per inch. The preferred GM Taber stiffness values for a fiber mat density of 3, 4.5, 6.5, 7, and 8.3 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch are respectively 0.0084 w2.63 /grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00043 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00024 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00021 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, and 0.00016 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, at a GM tensile value of 1323+24.2 w pounds per inch. At a paperboard fiber mat density of 3, 4.5, 6.5, and 7 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, the GM Taber stiffness values are as follows: 0.00120 w2.63 grams-centimeter/fiber mat density163 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00062 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00034 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, and 0.00030 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, and the GM tensile stiffness is 1890+24.2 w pounds per inch. The preferred GM Taber stiffness values for the foregoing fiber mat densities are 0.0084 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00043 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00024 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, and 0.00021 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, at the preferred GM tensile of 1323+24.2 w pounds per inch.
There is a further need for an efficient, economical method of ensuring a better distribution of bulk additives in paperboard intended for use in shaping containers and other products in which good insulating characteristics and deformability are desired.
There is a further need for bulk-enhanced paperboard whose manufacture does not cause fouling by unretained microspheres and which operates on conventional papermaking machinery without causing dryer sticking problems and without interfering with printing operations to which the paperboard may be exposed.
Accordingly, one object of the present invention is to provide a bulk-enhanced paperboard meeting the above needs in which a high percentage of bulk enhancing additives are retained and in which those bulk enhancing additives are substantially uniformly distributed in the resulting bulk-enhanced paperboard.
This is accomplished in one embodiment of the invention by providing a cellulosic paperboard web comprising predominantly cellulosic fibers; bulk and porosity enhancing additive interspersed with said cellulosic fibers in a controlled distribution throughout the thickness of the paperboard and size press applied binder, optionally including a pigment coating adjacent both surfaces of the paperboard web and penetrating into the paperboard web to a controlled extent. The overall fiber weight xe2x80x9cwxe2x80x9d of the web being at least 40 lbs. per 3000 square foot ream for less stringent requirements such as French fry sleeves. For other applications, the suitable range is 60 to 320 lbs. per 3000 square foot ream, advantageously 70 to 320 lbs. per 3000 square foot ream, and preferably 80 to 220 lbs. per 3000 square foot ream. Both the distribution of the bulk and porosity enhancing additive throughout the thickness of the paperboard and the penetration of the size press applied binder and optionally pigment coating into the board being controlled to simultaneously produce, at a fiber density of 3, 4.5, 6.5, 7, 8.3, and 9 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, a GM Taber stiffness respectively of at least about 0.00716 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, a GM tensile of 1890+24.2 w pounds per inch. The preferred GM Taber stiffness is 0.00501 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, and the preferred GM tensile stiffness is 1323+24.2 w pounds per inch. At a fiber mat density of 3, 4.5, 6.5, 7, and 8.3 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, GM Taber stiffness is 0.00120 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00062 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00034 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00030 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, and 0.00023 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, at a GM tensile stiffness of 1890+24.2 w pounds per inch. The preferred GM Taber stiffness values for a board having a fiber mat density of about 3, 4.5, 6.5, 7, and 8.3 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch are 0.0084 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00043 w2.63 grams-centimeter/fiber mat density 1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00024 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00021 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, and 0.00016 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, at GM tensile of 1323+24.2 w pounds per inch. At a fiber mat density of 3, 4.5, 6.5, and 7 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, the GM Taber stiffness values are 0.00120 w grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00062 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00034 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00030 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, and a GM tensile stiffness 1890+24.2 w pounds per inch. The preferred GM Taber stiffness values are 0.0084 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00043 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00024 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00021 w2.63 grams-centimeter/fiber mat density11.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, at a GM tensile of 1323+24.2 w pounds per inch.
The formable ultra rigid paperboard exhibits superior bending (GM Taber stiffness) and GM tensile stiffness. Usually, the paperboard has a bulking additive present. This bulking additive is selected from a group consisting of expanded or unexpanded microspheres, continuously or discontinuously coated expanded or unexpanded microspheres, thermally or chemically treated cellulose fibers rendered anfractuous and high bulk additive (HBA) fibers and mixtures of some or all of these bulking additives. The thermally or chemically treated fibers are disclosed in U.S. Pat. Nos. 5,384,011 and 5,384,012 assigned to the assignee of the instant patent application. Both of these United States patents are incorporated herein by reference in their entirety. Suitably the bulking additives, such as microspheres, are attached to the cellulose fiber prior to the formation of the embryonic web.
Microspheres are heat expandable thermoplastic polymeric hollow spheres containing a thermally activatable expanding agent. Such materials, the method of their manufacture, and considerable information concerning the properties and uses of microspheres are all set forth in the following U.S. Pat. Nos. 3,615,972; 3,864,181; 4,006,273; and 4,044,176. Microspheres are prepared from polyvinylidene chloride, polyacrylonitrile, poly-alkyl methacrylates, polystyrene or vinyl chloride. A wide variety of blowing agents can be employed in microspheres. Advantageously, commercially available blowing agents are selected from the lower alkanes such as propane, butane, pentane, and mixtures thereof. Isobutane is the preferred blowing agent for polyvinylidene chloride microspheres. Suitable microspheres are disclosed in U.S. Pat. Nos. 3,556,934; 3,293,114; and 4,722,944, all incorporated herein by reference. Suitable coated unexpanded and expanded microspheres are disclosed in U.S. Pat. Nos. 4,722,943 and 4,829,094, both incorporated herein by reference.
Suitably a retention aid is employed. The retention aid is selected from the group consisting of coagulation agents, flocculation agents, and entrapment agents. Flocculation and coagulation agents are the preferred retention aids. Advantageously a binder is utilized, usually in conjunction with a pigment. Suitable sizing agents are also employed. Suitably 1-30 pounds of sizing agent for a three thousand square foot ream are used for paperboards having a fiber mat density of about 3 to 8.3 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch. Advantageously, 6-30 pounds of sizing agent is used for a three thousand square foot ream of paperboard having a fiber mat density in excess of 8.3 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch. For certain special applications, 0-6 pounds of sizing agent is used for a three thousand square foot ream. Advantageously, about 15-30 pounds of the sizing agent is utilized. Preferably 16-19 pounds of the sizing agent is used for each three thousand square foot ream. The appropriate control of the amount of sizing agent added controls the GM tensile stiffness of the board. In the manufacture of the paperboard optionally wet strength agents are utilized. Parez 631 is a suitable wet strength agent. Other wet strength agents are FDA approved polyamides and acrylamides if the end use of the board is to be used as food containers and the wet strength agents come in direct contact with edible material.
Advantageously, the bulk enhanced paperboard is conveniently pressed into high quality articles of manufacture having a high GM Taber stiffness and GM tensile stiffness. Useful articles made from the bulk enhanced paperboard include cartons, folding paper boxes, cups, plates, compartmented plates, bowls, canisters, French fry sleeves, hamburger clam shells, rectangular take-out containers, food buckets, heat insulating containers coated or laminated with a polyolefin and foamed with the water contained in the fiberboard and food containers with a microwave susceptor layer. The articles of manufacture are characterized by having excellent insulation properties. These properties are critical for hot and cold cups and plates of this invention. The GM Taber stiffness and GM tensile stiffness for the one-ply web is the same as for the one-ply paperboard. For multi-ply boards, the GM Taber stiffness and GM tensile stiffness is the same as for the one-ply paperboard. The paperboard of this invention has at a fiber mat density of 3, 4.5, 6.5, 7, 8.3, and 9 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, a GM Taber stiffness of at least about 0.00716 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, and a GM tensile of 1890+24.2 w pounds per inch. The preferred GM Taber stiffness at a fiber mat density of 3-9 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch is 0.00501 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, and the preferred GM tensile stiffness is 1323+24.2 w pounds per inch. The GM Taber stiffness values for a paperboard having a fiber mat density of 3, 4.5, 6.5, 7, and 8.3 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, are 0.00120 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00062 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00034 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00030 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, and 0.00023 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, at a GM tensile stiffness of 1890+24.2 w pounds per inch. The preferred GM Taber stiffness values for a board having a fiber mat density of about 3, 4.5, 6.5, 7, and 8.3 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch are 0.0084 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00043 w grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00024 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00021 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, and 0.00016 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, at a GM tensile of 1323+24.2 w pounds per inch. At a fiber mat density of 3, 4.5, 6.5, and 7 pounds per 3000 square foot ream at a fiberboard thickness of 0001 inch, the GM Taber stiffness values are 0.00120 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00062 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00034 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, and 0.00030 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, at a GM tensile stiffness of 1890+24.2 w pounds per inch. The preferred GM Taber stiffness values are 0.0084 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00043 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, 0.00024 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, and 0.00021 w2.63 grams-centimeter/fiber mat density1.63 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, at a GM tensile of 1323+24.2 w pounds per inch.